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Subject[tip:core/rcu] rcu: Fix holdoff for accelerated GPs for last non-dynticked CPU
Commit-ID:  622ea685f1fafdf84d612440535c84341f0860b8
Gitweb: http://git.kernel.org/tip/622ea685f1fafdf84d612440535c84341f0860b8
Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Sat, 27 Feb 2010 14:53:07 -0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Sun, 28 Feb 2010 09:17:42 +0100

rcu: Fix holdoff for accelerated GPs for last non-dynticked CPU

Make the holdoff only happen when the full number of attempts
have been made.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1267311188-16603-1-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/rcutree_plugin.h | 8 +++++---
1 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 464ad2c..79b53bd 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1010,6 +1010,10 @@ int rcu_needs_cpu(int cpu)
int c = 0;
int thatcpu;

+ /* Check for being in the holdoff period. */
+ if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies)
+ return rcu_needs_cpu_quick_check(cpu);
+
/* Don't bother unless we are the last non-dyntick-idle CPU. */
for_each_cpu_not(thatcpu, nohz_cpu_mask)
if (thatcpu != cpu) {
@@ -1041,10 +1045,8 @@ int rcu_needs_cpu(int cpu)
}

/* If RCU callbacks are still pending, RCU still needs this CPU. */
- if (c) {
+ if (c)
raise_softirq(RCU_SOFTIRQ);
- per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
- }
return c;
}


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